Advertised prices on Hostelbookers etc

The hostels of SYHA typically have prices of £18.50 for a dorm bed, according to their own site. There's an additional £2 if you are not a member.

If you look for one of them through Hostelbookers you find them, on the page where they list hostels, as £12. Not even: "From £12". But when you come to book, the price you are quoted is £18.50.

On Hostelworld, at least one hostel of the above shows £20 as the price for a dorm bed.

Hostelbookers seem to not have this anomaly for other hostels, so this might be a failing of SYHA to correctly update their entries on Hostelbookers.